The invention concerns a method and a device for determining the quantity of product contained in a reservoir, for example in an ink reservoir for a printer, for example by measuring a resistance representing this quantity, preferably even when the reservoir is in a noise environment.
Methods have already been proposed for detecting the residual quantity of available ink contained in ink reservoirs within printing devices.
Some of these methods are based on a measurement of resistance variation.
Thus the document EP-A-0 370 765 describes a method for detecting the presence of an electrically conductive ink in the ink discharge pipe which connects a storage cavity of the reservoir to an ejection or print head. Two electrodes are placed in this pipe: an absence of ink in the pipe (because of the exhaustion of the ink contained in the cavity or because this ink has dried in the pipe, notably) is easily detectable by the abrupt increase in resistivity between the electrodes.
The document EP-A-0 509 747 for its part discloses disposing two electrodes in two zones of a porous body contained in the reservoir and soaked with the ink in question, these two zones being chosen so as to have different capillarities. The variations in the concentration of ink within the porous body has an influence on the resistivity of the area of the porous body between the electrodes, which makes it possible to detect the quantity of ink.
These methods have a certain number of defects, the main one of which is that installing the electrodes requires an adaptation of the reservoir (the term cartridge is sometimes used to designate the exchangeable assembly of which the reservoir forms part), namely its cavity or its discharge pipe. This gives rise to a certain degree of complexity and therefore an increase in the cost of producing the reservoirs or cartridges.
Moreover, these electrodes are in direct contact with the ink, which is often corrosive, which obliges the manufacture to use noble materials (gold, etc), which are therefore expensive.
Finally, the first aforementioned document does not afford a true determination of the residual ink, since it monitors only the resistive state of the pipe through which the ink flows, whilst the second document discloses only detecting the passing of a threshold or residual ink level without the user being able to know the quantity of ink remaining in the reservoir as long as this threshold has not been passed.
Other methods involve a measurement of apparent capacitance.
Thus for example the document EP-A-0 028 399 describes a detection method using an resonant circuit with which the reservoir to be monitored is integrated. More precisely, the capacitor of this resonant circuit has two metal plates forming electrodes defining a dielectric space in which the storage cavity of the ink reservoir is situated.
The ink thus behaves as a dielectric whose value changes as the ink reserve decreases. Consequently the capacitance of the resonant circuit also changes.
The latter is calibrated so that its resonant frequency, and therefore the maximum voltage at its resistor, is reached when the level of the ink reserve has dropped to a predetermined value. When this threshold is passed, a signal is activated.
This method has a certain number of defects.
When the ink level decreases, the voltage at the terminals of the resistor varies up to a certain threshold. The only information given by this device is therefore an indication on the situation (greater or not) of this level with respect to the threshold.
Only the information relating to the amplitude of the measurement signal is taken into account and compared with a threshold; this type of detector indicates only one type of information: when 20% of the ink remains in the reservoir. By using an analogue to digital converter, determining the level of ink in the reservoir continuously could be considered, but this type of component has a high cost.
In addition, when it is wished to measure the quantity of ink present in small reservoirs or when the capacitance is of low value (a few picofarads), the resonant frequency then becomes extremely high, which appreciably increases the cost of the components used and may generate electromagnetic interference. One solution would consist of using inductors of very high value (1 henry for example). These would reduce the frequency, but they are very difficult to produce and are bulky.
It is briefly mentioned in this document that it is possible to use a parallel circuit but it is added that a series circuit is preferable.
The ink plotters such as the one mentioned in the description have a reservoir and a recorder. The reservoir and recorder are not electrically connected to the printing device, which of course makes it possible to place the capacitor consisting of metal plates and ink reservoir in a series or parallel configuration.
Likewise, conventional wound inductors can be placed equally well in a series or parallel configuration.
It must nevertheless be noted that:
if the recorder is for example connected to a potential, for example earth, the series resonant circuit cannot be produced; this case is however increasingly usual;
if the capacitance is very small, it is necessary to produce inductors with very high values if it is desired to remain within low frequencies, which cannot be achieved in conventional technologies.
In any event, the known solutions are not suitable for dealing with cases where, at the time of the measurements, the reservoir and the associated detection means are in a noisy environment and because of that suffer interference leading to erroneous measurements.
A first object of the invention is to mitigate the aforementioned drawbacks by virtue of a method or device which allows the detection, at least within an operating range including preferably the low values, of the residual quantity of an electrically conductive product contained in a reservoir made of electrically insulating material, in a simple, precise and reliable fashion, by measuring a resistance characterising the reservoir when the latter is included in a resonant circuit, without having to modify the latter in any way.
A second object of the invention is to mitigate the aforementioned drawbacks by virtue of a method or device which allows the detection, at least within an operating range preferably including low values, of the residual quantity of an electrically conductive product contained in a reservoir made of electrically insulating material, in a simple, precise and reliable fashion, in particular by eliminating the effects of the environment, such as electromagnetic noise, and this by means of measurements which require no modification to the reservoir in order to fit electrodes.
Additionally (but these aspects can be taken into consideration independently of each other and of the aforementioned object) the invention aims to achieve this object:
even when the technological constraints of location and operation of the system receiving the reservoir allow the formation only of a resonant circuit of the parallel type (in particular when the reservoir includes, or cooperates with, a print head whose operation requires an electrical connection of the said head to a predetermined potential, which prevents any series connection);
at a moderate cost and within a moderate size, in particular without using components which are difficult to produce and/or expensive in the resonant circuit itself or in the generator designed to deliver excitation signals to this resonant circuit;
while easily allowing the detection also of situations where there is no product in a duct delivering product to a print or ejection head (therefore minimizing the additional components to be provided when it is desired not only to detect the quantity of product in a storage cavity of this reservoir but also to check, in real time, that there is indeed, in the delivery duct, product in a normal state, that is to say electrically conductive).
According to a first aspect, the invention proposes a method of determining the quantity of an electrically conductive product contained in a reservoir made of electrically insulating material having at least one storage cavity, according to which:
a resonant circuit is formed having a capacitive arrangement comprising at least part of this reservoir;
this resonant circuit is connected to an excitation signal generator;
a measurement procedure is defined according to which a plurality of excitation signals is applied to this resonant circuit having different frequencies included in a predetermined frequency range and a plurality of measurement signals are taken off at a measuring point in response to these excitation signals, this frequency range being chosen so as to contain the frequencies at which the resonant circuit is in resonance for a plurality of values of the quantity of product within a predetermined operating range;
a processing procedure is defined consisting of identifying the value of a characteristic of this resonant circuit from this plurality of measurement signals, deriving from this value of the characteristic a measurement of the resistance formed by the product contained in the reservoir in the said capacitive arrangement and deriving therefrom the instantaneous value of an item of information representing the quantity of product contained in the reservoir using a pre-established correlation law; and
at least one determination cycle is effected, consisting of triggering the measurement procedure and the processing procedure, and capturing the instantaneous value of the said item of information.
In fact, it is already known that attempts can be made to evaluate the quantity of product contained in a reservoir by exciting the resonant circuit with which there is integrated, within a capacitive arrangement, at least part of the reservoir (see for example the document EP-A-0 028 399), although this is generally for detecting only the fact that a minimum filling threshold has been passed. It is then the value of the capacitance formed by the reservoir within the resonant circuit which is of interest. However, assimilating the reservoir to a pure capacitance is a simplification of reality, so that it is more exact to take account, in the processing of the measurement signals, of the fact that the combination of two electrodes and a reservoir, at least part of which is disposed in the dielectric space defined by these electrodes, should be analysed as the connection in series of a resistance (represented by the product in the reservoir) between two capacitors (of substantially constant characteristics) each formed by one of the electrodes, the thickness of the wall of the chamber delimiting the cavity and the said product. This complicates the processing of the measurement signals, but in an entirely reasonable fashion, and leads to evaluations of the quantity of product which are much more precise.
The more the resistance between the capacitors varies greatly, which is notably the case when the cavity contains a porous body impregnated with the said product, the more such an electrical analysis of the reservoir in the resonant circuit is useful, and leads to measurements which are all the more precise. The invention is therefore particularly well suited to monitoring the consumption of the product when the latter impregnates a porous body disposed in the storage cavity of the reservoir; the capacitive arrangement then comprises part of this porous body.
The characteristic of the resonant circuit can quite simply be the amplitude of the resonance peak.
However, it may appear more precise to choose to evaluate the resistance from the measurement of the quality factor Q of this resonant circuit (the width of the resonance peak for a signal threshold representing the amplitude of the resonance peak reduced by 3 dB). It did in fact become clear that it varied univocally with the quantity of a product such as an ink.
According to a second aspect, the invention proposes a method of determining the quantity of an electrically conductive product contained in a reservoir made of electrically insulating material having at least one storage cavity, according to which:
a resonant circuit is formed, including a capacitive arrangement comprising at least part of this reservoir, this resonant circuit having at least two states;
this resonant circuit is connected to an excitation signal generator and to means adapted to cause the resonant circuit to change from a first to at least one other state;
a measurement procedure is defined according to which at least one excitation signal is applied to this resonant circuit and at least one measurement signal is taken off at a measurement point in response to this excitation signal, this excitation signal being chosen so that the measurement signal varies univocally with the quantity of product contained in the storage cavity;
for each state of the resonant circuit a processing procedure is defined, including a first step consisting of identifying, from this measurement signal or signals, the value of a characteristic of this capacitive arrangement, and a second step consisting of deriving therefrom the instantaneous value of an item of information representing the quantity of product contained in the reservoir from a pre-established law of correlation between values of this characteristic and values of the quantity of product in the storage cavity;
a verification procedure is defined consisting of comparing the value of this characteristic or of this item of information with a possible range of values; and
at least one determination cycle is effected, consisting of putting the resonant circuit in its first state, triggering the measurement procedure and optionally the processing procedure associated with this first state, then the verification procedure and, if the verification is positive, capturing the instantaneous value of the said item of information or, if not, demanding a change of state of the resonant circuit when this verification procedure detects that the value is outside its range and once again triggering the measurement procedure and then the processing procedure for this new state of the resonant circuit and capturing the new instantaneous value of the said item of information.
Thus, in summary, the invention proposes to dispose at least part of the reservoir in a capacitive arrangement within a resonant circuit, to excite this circuit so as to be able to evaluate a characteristic of this circuit, to derive therefrom the instantaneous value of an item of information representing the quantity of product in the reservoir but, before ending the processing of the measurement signal or signals, to check that the quantities involved in this processing are plausible; if this test is positive the processing is continued (if it was not ended at the time of the test), but if this test is negative the resonant circuit is modified before commencing once again to excite the resonant circuit, to evaluate a characteristic of this circuit in its new state, and to derive therefrom the required information.
Preferably, there is a plausibility test which is triggered during the processing (or at the end thereof), not only when the resonant circuit is in its first state, but also after it has changed state following a first negative test. Preferably, in order to deal with cases where the second plausibility test is also negative, the resonant circuit is advantageously designed so as to allow a third state (more generally, there may be a plurality of possible states which are tested successively until it is found that the plausibility test becomes positive). However, it is preferable to trigger the verification procedure with regard to each processing, and thus avoid giving a result which may be false.
In fact, it appeared that the noise liable to falsify the results is generally electromagnetic noise in a very narrow frequency band: this may lead to aberrant results when the resonant circuit is excited in this frequency band, with the appearance of xe2x80x9cfallaciousxe2x80x9d resonances. However, it suffices to modify the resonant circuit so that the resonant frequencies corresponding to the possible concentrations of product become substantially separate from the frequency band of the noise: the latter is then neutralised and the results can be considered to be reliable. It suffices to design the excitation signal generator so that it is capable of generating signals with frequencies contained in the various frequency ranges in which the circuit can come into resonance as a function of its state.
The resonant circuit can be modified by acting on an element whose capacitance or inductance is variable. It is however much simpler and less expensive to make provision for this modification to take place by simple substitution or by simple addition of components, by acting on simple switches.
The measurement procedure preferably includes the application to the circuit of a plurality of signals having different frequencies, in a frequency band containing the resonant frequencies of the resonant circuit for various values of the quantity of product.
Preferably, the verification procedure consists of testing the plausibility of the information, rather than that of an intermediate quantity: this thus tests the correct progress of the processing procedure itself.
The characteristic of the resonant circuit which is identified can notably be the capacitance formed by the reservoir in the capacitive arrangement: it can easily be evaluated, for example by detecting the amplitude of the resonance peak or by another characteristic of this peak.
However, it may turn out to be more precise to seek to evaluate the resistive component of the capacitance (in the broad sense of the term) formed by the reservoir in the capacitive arrangement.
However, assimilating the reservoir to a pure capacitance is a simplification of reality, so that it is more exact to take account, in the processing of the measurement signals, of the fact that the combination of two electrodes and a reservoir, at least part of which is disposed in the dielectric space defined by these electrodes, should be analysed as the connection in series of a resistance (represented by the product in the reservoir) between two capacitors (of substantially constant characteristics) each formed by one of the electrodes, the thickness of the wall of the chamber delimiting the cavity and the said product. This perhaps complicates the processing of the measurement signals, but in an entirely reasonable fashion, and leads to evaluations of the quantity of product which are much more precise.
The more the resistance between the capacitors varies, which is notably the case when the cavity contains a porous body impregnated with the said product, the more such an electrical analysis of the reservoir in the resonant circuit is useful, and leads to measurements which are all the more precise. The invention is therefore particularly well suited to monitoring the consumption of the product when the latter impregnates a porous body disposed in the storage cavity of the reservoir.
The modification of the resonant circuit is advantageously achieved by modifying a component of the notional inductor (when it is present), for example by modifying the capacitance, taking advantage of the amplification effect which is produced, for example, by the gyrator circuit.
One of the possible sources of cost in implementing the methods of the invention lies in the need to be able to generate excitation signals at frequencies close to the resonant frequency. Preferably, when possible, the invention is implemented in the range of low or medium frequencies (approximately 1 kHz to approximately 100 kHz). This can sometimes be easily achieved, having regard to the nature of the product and the geometry and dimensions of the reservoir, by using conventional components for producing the resonant circuit.
In the field of printing machines the capacitance values typically encountered with ink reservoirs lead on the other hand to resonant frequencies in the field of high frequencies (beyond around 1 megahertz), unless it is possible to use inductors of very high values which, when they exist, are very expensive.
The advantage of using, according to a preferred characteristic of the invention, a notional inductor is that it is possible to simulate high-value inductors easily without using components which are complex or difficult to produce. A so-called xe2x80x9cgyratorxe2x80x9d circuit is thus known which, with a few resistors and two amplifiers, makes it possible to simulate a high constant inductance using a constant capacitance of conventional value (typically around scarcely a few picofarads) of moderate cost and bulk. However, it became clear that installing such resistors and such amplifiers entailed in itself only a moderate increase in cost and bulk, so that such a gyrator led itself very well, in spite of appearances, to forming notional inductors of high value at a cost and within an overall bulk which were entirely moderate, including when operating in the field of office printing machines. The invention makes it possible, as desired, to dispose the reservoir in the capacitive arm or in the inductive arm of the resonant circuit, but location in the capacitive arm may be preferred since it leads to a fairly easy processing procedure; the capacitive arrangement and the notional inductor are therefore advantageously distinct from each other.
It may be noted that the method (in its two aspects) lends itself very well to a parallel connection of the capacitive and inductive components of the resonant circuit, which makes it applicable to any type of reservoir, whatever the type of associated ejection or print heads. For reasons of simplicity or to meet operating constraints, these components are advantageously connected between a measuring point and earth.
Preferably, the capacitive arrangement includes two metallic parts forming the electrodes of a capacitor, one of which is disposed in the immediate vicinity and opposite a portion of the storage chamber of the reservoir, and the other one of which is formed by, or connected to, an ejection or print head connected to the storage chamber by a connecting or delivery duct, by virtue of which the capacitive arrangement takes account not only of the quantity of product in the chamber but also in the connecting duct. Such an assembly makes it possible to add, to the parts necessary for the operation of the head, only a single metal part.
The operation of certain print heads currently known makes it necessary for the latter to be connected to earth: this is why, the resonant circuit then being of the parallel type, the print or ejection head is advantageously connected to a reference potential formed by earth.
The invention applies notably to the case of printing machines using a reservoir, generally removable, containing an electrically conductive ink: the resonant circuit, including the first electrode, is then advantageously fixed with respect to the casing of the printing machine.
It is very easy to adapt the method of the invention for monitoring the state of the product in the delivery duct, whether there is a lack of it, or whether it dries up, notably. The characteristics of the capacitive arrangement, when the latter includes the delivery pipe, are then fundamentally modified, leading in practice to values, whether before or after processing, which are entirely different from the values which can normally be obtained: it suffices to provide for a test in this regard and an abnormality procedure (excitation of an audible or light signal for example) to be triggered as appropriate.
It is clear that the information concerning the quantity of product can be of at least two natures, depending on whether concern is with the quantity already consumed or the residual quantity.
The excitation signals are preferably alternating signals, but can also, in a variant, be square-wave or pulsed signals.
The invention also proposes, for implementing the first method, a device for determining the quantity of an electrically conductive product contained in a storage cavity made of electrically insulating material, having:
a resonant circuit including a capacitive arrangement designed to comprise at least part of this reservoir, this circuit having, for various possible values of the quantity of product contained in a given operating range, resonant frequencies contained within a predetermined frequency range;
an excitation signal generator connected to the resonant circuit and adapted to generate various frequencies belonging to this predetermined range;
measurement and processing means connected to this resonant circuit and to the excitation signal generator and designed so as to apply to the resonant circuit a plurality of excitation signals having various frequencies within the said predetermined range, to detect a measurement signal in response to each excitation signal, and to identify from this plurality of measurement signals the value of a characteristic of this resonant circuit, to derive from this value of the characteristic a measurement of the resistance formed by the product contained in the reservoir in the said capacitive arrangement and to derive therefrom the instantaneous value of an item of information representing the quantity of product contained in the reservoir from a pre-established correlation law; and
means for capturing the instantaneous value of the said information.
The invention further proposes, for implementing the second method, a device for determining the quantity of an electrically insulated product contained in a storage cavity of a reservoir made of electrically conductive material, having:
a resonant circuit including a capacitive arrangement designed to comprise at least part of this reservoir, this circuit having at least a first state and a second state;
control means for causing this resonant circuit to change from the first state to the second state;
an excitation signal generator connected to the circuit;
measurement and processing means connected to this resonant circuit, to the excitation signal generator and to the control means, and designed so as to apply at least one excitation signal to the resonant circuit, to take off a measurement signal in response to each excitation signal, to identify the value of a characteristic of this capacitive arrangement and to derive therefrom an item of information representing the quantity of product contained in the storage cavity using a pre-established correlation law;
verification means designed so as to compare the value of this characteristic or of this item of information with a range of possible values;
determination means designed so as to put the resonant circuit in its first state, to trigger the measurement procedure and optionally the processing procedure associated with this first state, and then the verification procedure, and;
if the verification is positive, to capture the instantaneous value of the said item of information;
or otherwise to demand a change of state of the resonant circuit when this verification procedure detects that the value is outside its range and to trigger once again the measurement procedure and then the processing procedure for this new state of the resonant circuit and to capture the new instantaneous value of the said item of information.
The same comments as before apply to the device thus defined.
The invention also concerns a signal processing device formed by measurement and processing means and means for capturing the instantaneous value of the information sought.
The invention applies finally to:
a product supply device combining a device for determining the quantity of product with the reservoir and the means of controlling the ejection head;
the particular case, important in practice, where this product supply device is an image forming device;
a printing system including only the device for determining the quantity of product with the reservoir, in the case of an ink reservoir;
an office machine including any one of the aforementioned devices; and
an office signal processing unit designed to cooperate with an ink reservoir and including a processing device of the aforementioned type;
a means, fixed or partially or totally removable, of storing information which can be read by a computer or microprocessor storing instructions of a computer program, characterised in that it enables the methods of the invention as briefly disclosed to be implemented, and
a means, fixed or partially or totally removable, of storing information, which can be read by a computer or a microprocessor storing data resulting from the implementation of the methods as briefly disclosed above.
It will be appreciated that, according to the first aspect, the invention makes it possible:
to establish a univocal relationship between the quantity of ink remaining and the value of the resistance calculated by means of the quality factor or the signal amplitude at the resonant frequency,
to produce a level-measurement system integrated into the print device and requiring no modification to the ink cartridge;
to reduce the bulk of the mechanical configuration by using the print head as the second plate of the capacitor;
to use low excitation frequencies by means of an appropriate choice of the components of a circuit of the gyrator type as an inductor.
It will be appreciated that, according to the second aspect, the invention seeks to determine a frequency range where the ambient noise does not interfere with the measurement of the quantity of product.
It can use a linear relationship between the remaining quantity of ink and the value of the resistance calculated by means of the quality factor or the signal amplitude at the resonant frequency.
It makes it possible to reduce the bulk of the mechanical configuration by using the print head as the second plate of the capacitor.
It can be implemented with low or medium frequencies by using a circuit of the gyrator type as an inductor.
It can use, in a variant, a univocal relationship between the remaining quantity of ink and the value of the capacitance calculated from the resonant frequency.